Studies conducted in our laboratory have indicated the feasibility of producing long acting methadone tablets. Using the same procedures sustained release forms of the following methadone derivatives will be attempted: (a) methadone-a-naphthalene, (b) methadone-o-benzoylbenzoic acid and (c) mixtures of methadone-naloxone. Derivatives (a) and (b), considered to be slowly-dissolving compounds, shall also be examined for their prolonged action as suspension dosage forms. In vitro and in vivo evaluation of the sustained release action of the above prepared formulations will be carried-out using dissolution studies and elevation of pain threshold (in rats) techniques respectively. The determination of long acting methadone metabolites in urine will be attempted. It is our belief that a successful sustained release formulation (3 days and over) can subsequently be used for the maintenance treatment of narcotic addicts.